The list -.+./t appended to any classification
table t will yield a complete classification table,
and the function defined below therefore completes a classification table.
The function tab ensures that a scalar or
vector argument is treated as a one-rowed table.

A function that yields a single boolean list is called a
proposition; its result is a one-way classification
called a set. The classification can, of course,
be completed by the complementary set. For example: